Hi meepers, I am trying to use MEEP to calculate the transmission and reflection spectra of a 1D grating. But I found their sum is not exactly 1. I used 2D geometry that is infinity in z-direction, Bloch-periodic boundary condition in X direction, pml in Y direction. The only dielectric is a block of epsilon=9, which is one grating unit. Gaussian point source is placed far away from the grating. The reflection and transmission flux collectors are place 0.5 wavelength above and below the grating. The image is attached, blue is transmission, red is reflection, magenta is their sum. The .ctl file is below my signature. I will appreciate if someone can provide any useful information!
--
Sincerely,
Zhaorong Wang
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;;;;;; In this case, I put the source far away from the grating so
that it becomes plane wave
;;;;;; upon the grating. And the source is also away from the pml so
that it will not
;;;;;; disturb the flux collecting.
(define-param sx 5.85) ; Size of cell in X direction
(define-param sy 50) ; Size of cell in Y direction
(define-param bottom (* -0.5 sy)); Y coordinate of bottom of the cell
(define-param top (* 0.5 sy)) ; Y coordinate of top of the cell
(define-param left (* -0.5 sx)) ; X coordinate of left of the cell
(define-param right (* 0.5 sx)) ; X coordinate of right of the cell
(define-param pad 8) ;pad thickness from the top to the source
(define-param lamb 8.0) ; wavelength in vacuum
(set! geometry-lattice (make lattice (size sx sy no-size)))
(define-param h 1.25) ; Height of the grating layer
(define-param w 2.0475) ; width of a grating unit
(define-param no-grating false) ; if true, have no grating structure
(set! geometry
(if no-grating
(list )
(list
(make block
(center 0 (+ bottom (* 2 lamb)))
(size w h infinity)
(material (make dielectric (epsilon 9)))))))
(set! k-point (vector3 0 0 0))
(set! ensure-periodicity true)
(define-param fcen 0.125) ; pulse center frequency
(define-param df 0.07) ; pulse width (in frequency)
(set! sources (list
(make source
(src (make gaussian-src (frequency fcen) (fwidth df)))
(component Ez)
(center 0 (- top pad)) ; pad from the top
)))
(set! pml-layers (list (make pml (thickness 1.0)(direction Y))))
(set-param! resolution 10)
(define-param nfreq 100) ; number of frequencies at which to compute flux
(define trans ; transmitted flux
(add-flux fcen df nfreq
(make flux-region
(center 0 (+ bottom (* 1.5 lamb) )) (size w 0))));
0.5 lambda from grating
(define refl ; reflected flux
(add-flux fcen df nfreq
(make flux-region
(center 0 (+ bottom (* 2.5 lamb) )) (size w 0))));
0.5 lambda from grating
(if (not no-grating) (load-minus-flux "refl-flux" refl))
(run-sources+
(stop-when-fields-decayed 50 Ez (vector3 0 (+ bottom (* 1.5 lamb))) 1e-3)
(at-beginning output-epsilon)
(to-appended "ez" (at-every 1 output-efield-z)))
(if no-grating (save-flux "refl-flux" refl))
(display-fluxes trans refl)
<<attachment: rsl_10.png>>
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